Laminated glass is widely used in construction, automotive windshield and other fields. It is made of two pieces of glasses (which may be flat or curved) with a layer of special film glue in sandwiched therebetween. VPL (Vacuum Process Line) is an important link in the laminated glass production line. Typically, for the two pieces of glass to bond well together, the vacuum between them must be high, and the glass need to be heated between 120-140° C. at such vacuum condition for a period of time. Thus, the maintenance of high vacuum is crucial for the production of laminated glass.
There is no automatic online detection for the vacuum in the pairs of glass panels in existing production lines of laminated glass. Whether the desired level of vacuum is maintained in the actual operation of the production line is largely left to the experience of the operators (they often make the determination whether there is a vacuum leak by listening to the sound of the production line), or by using a pressure gauge at the main vacuum suction pipe to monitor possible vacuum leak. If only some sections of the glass have vacuum leak while other sections are intact, this detection method would often fail to detect the leak. Furthermore, because the vacuum line for all paired units of glass panels is connected, a vacuum leakage anywhere in the production line would affect many other units in the product line, resulting in batch of products not meeting the production standard. Thus, the yield of finished products meeting the quality standard of the finished products is low.